Process for producing a three dimensional object from particles, as well as product produced thereby

ABSTRACT

Generative processes for production of a three dimensional object comprised of particles are increasingly employed in the manufacture of casting molds and casting cores. Therein the casting mold is constituted of sand particles, which are joined using a binder material. The task of the present invention is comprised therein, of providing an alternative layer building-up process for production of a three dimensional object, which achieves sufficient casting stability, without suffering intolerable quality degradation due to evolution of off-gases from binder material during casting. This task is solved by a process employing particles, which are comprised of a mono- or polyvalent, water and/or alcohol soluble metals salt.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the priority under 35 U.S.C. § 119 of German patent application DE 10 2005 019 699.3, filed on Apr. 28, 2005.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention concerns a process for producing a three dimensional object from particles, as well as a object produced thereby. A generic process of this type is known for example from WO 2004/112988A2.

2. Description of Related Art

Generally, the known processes for producing a three dimensional object from particles are increasingly employed for manufacture of casting molds and casting cores. Therein the casting shape is built up of sand particles, which are joined by means of binder materials. Conventionally, organic binders are employed. These however decompose during casting due to the heat, whereby the quality of the produced component can be deteriorated. Thus, it is proposed in WO 2004/112988A2 to join the sand particles with a salt crystal binder material and/or protein binder material.

SUMMARY OF THE INVENTION

The task of the present invention is comprised in providing an alternative layer-building type process for producing a three-dimensional object, as well as a therewith produced object, which achieves sufficient cast strength, without causing unacceptable deterioration in quality due to off-gassing of binder material during casting.

This task is solved by the use of particles, which are comprised of a mono- or polyvalent, water and/or alcohol soluble metal salt.

Therein the inventive process for production of a three dimensional object includes the following steps:

application of a layer of particles upon a target surface,

spraying a selected part of the layer, corresponding to a cross section of the object, with a stream of liquid, which contains water and/or alcohol, so that the particles are joined in the selected part,

repeating the steps of application and radiation for a number of layers, such that the adjacent layers join in order to form the object,

wherein particles are employed, which are comprised of at least one mono- or polyvalent, water and/or alcohol soluble metal salt.

The term “liquid spray” herein includes not only one or more continuous or interrupted streams, but rather also individual droplets.

In the inventive process, in contrast to WO 2004/112988A2, sand particles, which there represent the essential structure forming element, are completely dispensed with. Surprisingly, it has been found that particles of mono- or poly-valent, water and/or alcohol and soluble metal salts, subsequent to appropriate spraying, already have a structural rigidity sufficient to meet the requirements for a number of casting applications.

Beyond this, the water and/or alcohol solubility of the entire particle, in contrast to the corresponding solubility of essentially only a small binder component, offers the advantage, that the diffusion of solvent into the surrounding particle bed is reduced or even completely prevented, whereby a substantially sharper border or delineation of the sprayed and unsprayed areas result, and therewith the time and effort invested in the subsequent follow-up processing can be substantially reduced.

Advantageous to the invention is the employment of lower alcohols (chain length ≦4), since they are simpler to work with, and in particular ethanol due to its better environmental compatibility.

According to an advantageous embodiment of the inventive process, at least one metal salt includes crystal water and/or at least one metal salt exhibits condensable anions.

Metal salts with crystal water are characterized by good water solubility, for example, NaCl, CuSO₄, or Al₂ (SO₄)₃.

Metal salts with condensable anions (for example with OH— or ethanol-groups) are characterized by increased brown stability, for example, NaAl (H₂PO₄)₃, K₂SiO₃, Na₂SiO₃, Na₂(HPO₄) or Na₃(HPO₄). First, they absorb the solvent and show a good green stability. Upon warming, a condensation reaction occurs, of which the reaction products could cause severe defects or gas inclusions during casting. Thus—just as in the case of metal salts with crystal water—first, a removal of the solvent by heating is necessary, from which the brown body results.

The condensation reaction can be accelerated by the presence of oxides (for example, CuO, Cu₂O, Al₂O₃, MgO) or hydroxides (for example Al(OH)₃). Na₂(HPO₄) or Na₃(HPO₄) are water and alcohol soluble.

It is advantageous to include additives for modifying the surface tension of the melt of the particles, for example, calcium phosphate salts, which increase the surface tension of an aluminum melt and thereby ensure a smooth surface of the cast part.

An object made of particles joined together, which is produced by means of the inventive process, is particularly suited for employment as cast mold or cast core or also as tool or insert for plastic or ceramic mold shaping.

In particular, due to their water and/or alcohol solubility, cast cores or inserts can be easily disrupted and thereafter removed by spraying with their solvent.

DETAILED DESCRIPTION OF THE INVENTION

In the following the inventive process and the therewith produced object will be described in greater detail on the basis of two illustrative embodiments:

According to a first illustrative embodiment, in a conventional 3D printing process using a mixture of NaCl (65 wt. %) and MgSO₄ (35 wt. %) particles with a diameter between 30 and 100 μm, a casting mold was built up by spraying with water as a solvent in accordance with a convention 3D printing process. The thickness of the individual print layers was approximately 125 μm.

The casting mold had a green stability of approximately 0.75 MPa. It was heated for approximately two hours at 400° C. and exhibited thereafter a brown stability of 0.62 MPa. The finish processing time and effort was minimal. A simple blowing off of loose particle materials with weak compressed air was sufficient.

The test of the casting mold tempered to room temperature with an A356 aluminum alloy casting material at a casting temperature of 730° provided a good casting result with good surface quality. The mold itself was easily removed by dissolving in water for a short time.

According to a second illustrative embodiment, in a conventional 3D printing process, using a mixture of Al (H₂PO₄)₃ 27 wt. % (condensable water soluble salt); MgSO₄ (15.7 wt. %) (water soluble salt with crystal water); CuO 6.1 wt. % and Al₂O3, 6.1 wt. % (oxide as accelerator for the condensation reaction); Ca₅(PO₄)₃OH 5.9 wt. % (surface tension modifier for Al-melt) and Na₂(HPO₄) 39.2 wt. %, a casting core was built up by spraying with water as solvent according to a conventional 3D printing process. The powder mixture had a particle diameter of approximately 300-400 μm. The thickness of the individual print layers was approximately 125 μm.

The casting core had a green stability of approximately 3 MPa. It was heated for approximately two hours at 400° C. and exhibited thereafter a brown stability of 2.5 MPa. This suffices for employment as casting core. The finishing effort was minimal. A simple blowing off of the loose particle material with a compressed air strain was sufficient.

The test of the casting mold tempered to room temperature, casting with the aluminum alloy A266 at a casting temperature of 710° C., provided a good cast result with a good surface. The mold itself was easily removable by dissolving in water for a short period of time.

The inventive process and the therewith produced casting mold demonstrated themselves in the illustrative embodiments of the above-described examples as particularly suited for metal casting, in particular for aluminum precision casting, in the automobile industry.

In particular, substantial advantages can be achieved with regard to the quality of the internal surfaces.

The invention is not limited to only the above-described illustrative embodiments, but rather can be broadly applied.

Thus, the surface quality could be further improved by the addition of supplemental surface modifiers. 

1-6. (canceled)
 7. A process for producing a three dimensional object comprising the following steps: a. applying a layer of particles comprised of at least a mono- or polyvalent water and/or alcohol soluble metal salt upon a target surface, b. spraying a select part of the layer, corresponding to a cross section of the object, with a liquid stream containing water and/or alcohol, so that the particles are joined in the selected part, c. repeating steps a and b so that the joined parts of the adjacent layers combine to form the object.
 8. A process according to claim 7, wherein at least one metal salt having crystal water and/or at least one metal salt having condensable anions is employed in step a.
 9. A three dimensional object produced by a process comprising the following steps: a. applying a layer of particles comprised of at least a mono- or polyvalent water and/or alcohol soluble metal salt upon a target surface, b. spraying a select part of the layer, corresponding to a cross section of the object, with a liquid stream containing water and/or alcohol, so that the particles are joined in the selected part, c. repeating steps a and b so that the joined parts of the adjacent layers combine to form the object.
 10. The three dimensional object according to claim 9, wherein the object is a casting mold or casting core.
 11. The three dimensional object according to claim 9, wherein the object is a tool or an insert for a plastic or ceramic mold.
 12. A process for casting metal, comprising a. forming a casting mold by a process comprising (i) applying a layer of particles comprised of at least a mono- or polyvalent water and/or alcohol soluble metal salt upon a target surface, (ii) spraying a select part of the layer, corresponding to a cross section of the object, with a liquid stream containing water and/or alcohol, so that the particles are joined in the selected part, and (iii) repeating steps a and b so that the joined parts of the adjacent layers combine to form a green casting mold, b. heating the casting mold to form a brown casting mold, and c. casting a molten metal into said casting mold. 